Playing melody notes while cross picking is doable, I play Wildwood Flower and Banks of the Ohio in cross picking patterns. Also flatpick and using middle finger as a pinch is a technique used by many guitarists, George Harrison used it a lot also Roger McGuin of Byrds fame used flatpick and finger picks on middle and ring fingers. I have heard it referred to as chickin' pickin'.

The best recommendation I can give you Deborah is to check out Jerry Silverman's groundbreaking Oak Publication on Flatpick Guitar which give chapter and verse and instruction on cross picking? Forget Roger McGuinn Deborah, the late George Shuffler invented cross picking and you will find UTube videos of him demonstrating his technique